1. Field of the Invention
The present invention relates to a fuel injection valve whose injection amount and timing are adjusted in such a manner that a control valve controls fuel pressure of a pressure control chamber.
2. Description of the Prior Art
A conventional fuel injection valve, which is applied to an accumulated pressure type fuel injection system, has a pressure control chamber to which high pressure fuel accumulated in a common rail is supplied, a throttled fuel ejecting passage through which the high pressure fuel is ejected, and an electromagnetic valve operative to open and close the throttled fuel ejecting passage. With this electromagnetic valve, injection amount and timing of the fuel injection valve are adjusted by controlling fuel pressure of the pressure control chamber.
The conventional fuel injection valve has a drawback that, when fuel of the pressure control chamber is ejected via the throttled fuel ejecting passage under conditions that both of fuel temperature and pressure are relatively low, fuel flow state is not uniform and is likely to change between turbulent flow and laminar flow. As a result, fuel injection in each injection cycle is unstable and each injection amount tends to fluctuate.
It is an object of the present invention to provide a fuel injection valve in which a flow state of fuel ejected from a pressure control chamber via a throttled passage does not change between turbulent and laminar flows, resulting in less fluctuation of injection amount per each cycle.
To achieve the above object, in a fuel injection valve, a nozzle is provided with an injection bore and has a needle axially movable for opening and closing the injection bore. Fuel pressure in a pressure control chamber, to which high pressure fuel is supplied, is operative to urge the needle in a direction of closing the injection bore. A fuel flow-out passage is provided at an outlet thereof with an orifice through which the high pressure fuel introduced thereto from the pressure control chamber is ejected, when a control valve opens the fuel flow-out passage.
With the fuel injection valve mentioned above, the fuel flow-out passage is further provided with a guide member that, when the outlet thereof is opened by the control valve, guides a flow of the fuel introduced thereto from the pressure control chamber in such a manner that one of two flow states consisting of a turbulent flow state and a laminar flow state is exclusively formed at first and, then, maintained, always as far as fuel temperature is within a range from xe2x88x9230 to 80xc2x0 C. and fuel pressure is within 10 to 50 M Pa.
It is preferable that the orifice has a smooth cylindrical straight portion whose inner diameter is smaller than that of the fuel flow-out passage on an upstream side thereof, and the guide member is turbulent flow formation means for forcibly forming the turbulent flow state before the fuel introduced into the fuel flow-out passage from the pressure control chamber reaches the smooth cylindrical straight portion of the orifice and turbulent flow maintenance means for maintaining the turbulent flow state thus formed throughout the smooth cylindrical straight portion.
In this case, it is preferable that dimension of the smooth cylindrical straight portion, which constitutes the turbulent flow maintenance means, satisfies a formula, L/Dxe2x89xa61.2, where D is inner diameter of the smooth cylindrical straight portion and L is axial length of the smooth cylindrical straight portion.
As one of the turbulent flow formation means, the orifice is provided around a periphery of an inlet opening immediately adjacent the smooth cylindrical straight portion thereof with an inlet circumferential edge with which the flow of the fuel introduced into the fuel flow-out passage from the pressure control chamber is swirled so that the turbulent flow state is forcibly formed. In this case, dimension of the inlet circumferential edge of the orifice satisfy a formula, R/Dxe2x89xa60.2, where R is corner radius of the inlet circumferential edge and D is the inner diameter of the smooth cylindrical straight portion.
As another one of the turbulent flow formation means, the fuel flow-out passage including the orifice is provided in an interior thereof on an upstream side of the smooth cylindrical straight portion with projections or recesses with which the flow of the fuel introduced into the fuel flow-out passage from the pressure control chamber is disturbed so that the turbulent flow state is forcibly formed.
As further one of the turbulent flow formation means, the fuel flow-out passage including the orifice is provided in an interior thereof on an upstream side of the smooth cylindrical straight portion with a flow disturbance member with which the fuel introduced into the fuel flow-out passage from the pressure control chamber is stirred so that the turbulent flow state is forcibly formed.
As still further one of the turbulent flow formation means, the fuel flow-out passage including the orifice is provided in an interior thereof on an upstream side of the smooth cylindrical straight portion with a bending portion or a step portion whose diameter is stepwise changed, with which the fuel introduced into the fuel flow-out passage from the pressure control chamber is guided to flow in a curve so that the turbulent flow state is forcibly formed. A plurality of the turbulent flow formation means mentioned above may be combined with each other.
On the other hand, when the orifice has a smooth cylindrical straight portion whose inner diameter is smaller than that of the fuel flow-out passage on an upstream side thereof, the guide member maybe laminar flow formation means for forcibly forming the fuel introduced to the fuel flow-out passage from the pressure control chamber to the laminar flow state in the smooth cylindrical straight portion on an upstream side thereof and laminar flow maintenance means for maintaining the fuel thereof in the laminar flow state thus formed throughout the smooth cylindrical straight portion on a downstream side thereof.